Multilayer coextrusion offers many unique design possibilities in the world of plastics. There are many established technologies for the creation of flat films with tens to thousands of layers. Such technologies generally utilize a feed-block which will either create the layers of polymer through layer by layer addition or create a layer pattern and then multiply it through a layer multiplication technique, or through some combination of the two.
With the ability to create microlayers comes the ability to create unique structures with a multi-component approach of merging separate streams of plastic together. This combined stream could also undergo a multiplication technique to create new layered streams.
Conventional extrusion formed products are limited to approximately twelve layers. Multistream/multilayer extrusion processes can extend these limitations. Extrusion technologies are well known in the art examples of which are described in U.S. Pat. Nos. 6,669,458, 6,533,565 and 6,945,764, and are commonly owned by the assignee of the instant application. Micro-layer extrusion processes are specialized extrusion methods that provide products with small grain features such as described in U.S. Pat. No. 7,690,908, (hereinafter the “'908 Patent”) and U.S. Patent Publication 2012/0189789 (hereinafter the “'789 Publication”) both of which are commonly owned by the assignee of the instant application, the disclosures of which are incorporated herein by reference in their entirety.
Typical micro-layer products are formed in a sheet. If a tubular product is desired, the microlayer is first extruded as a sheet and then made into the tube. This creates a weld line or separation between the microlayers. The '908 Patent describes a cyclical extrusion of materials by dividing, overlapping and laminating layers of flowing material, multiplying the flow and further dividing, overlapping and laminating the material flow to generate small grain features and improve properties of the formed product. The '789 Publication describes extruding a flow of extrusion material in a non-rotating extrusion assembly, forming a first set of multiple laminated flow streams from the extruded flow, amplifying a number of the laminations by repeatedly compressing, dividing and overlapping the multiple laminated flow streams, rejoining the parallel amplified laminated flows, forming a first combined laminate output with micro/nano-sized features from the rejoining; and forming a tubular shaped micro-layer product from the combined laminate output.